Pin Map : UART pin on the 4-pin CON5 connector

Another UART port on 40pin header

If you don't use an I2C interface(i2c-1) on pin#3 & pin#5, you can use them to activate the UART2.
Just follow campbell's development note to have a new UART2 port via /dev/ttyS2.
Note that Pin#3(SDA1) is mapped to Tx and Pin#5(SCL1) is Rx.How to enable a third UART ttyS2 by "campbell"

Automatically configure the UART settings.

This is an example of default setting for a GPS module which has a 9600bpsN81 UART interface.
Add the following to the end of /etc/rc.local (before the exit 0)

/bin/stty -F /dev/ttyS2 raw 9600 cs8 clocal -cstopb > /dev/null 2>&1

This way the tty port is setup for use with the gps on system boot, without user interaction.